While not many specifics are yet known, on account of it just being publicly revealed today and all, the film is set to be written by Snowfall's Malcolm M. Mays.
The original New Jack City had a pretty noteworthy cast made up, in part, of: Wesley Snipes, Chris Rock, Flavor Flav, Judd Nelson, and Ice-T.
Its plot saw Wesley Snipes starring as a rising (and ruthless) drug kingpin, Nino Brown, who transformed a Harlem apartment complex into a well-defended base/crackhouse during the '80s crack epidemic. Ice-T and Judd Nelson play cops who eventually go undercover in an effort to bring Brown down. While Rock played an ex-stick-up kid who turns into a homeless drug addict (and eventually an informant) after he's shot in the ankle by Ice-T's character.
There's a lot more to it than that but it seems unwise to divulge the entire plot for a movie that's going to be re-released. Plus, if you haven't seen it and you're interested enough, there's about 100 ways to watch movies now so it's probably available to you somewhere.
During it's '91 release New Jack City made nearly $48 million off an $8 million budget. At the moment no director is attached to the reboot.
In the meantime, check out the trailer for the original version below: